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breaking bolts loose?

11-25-2008, 04:31 PM

I need to replace the exhaust manifolds on my truck in the near future. Both have cracks. It is a chevy 454. I can't get the bolts that hold them onto the heads to break loose, any hints? These are bolts not studs. I've only tried when the engine was cold. No way to get penetrating oil in there.

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I need to replace the exhaust manifolds on my truck in the near future. Both have cracks. It is a chevy 454. I can't get the bolts that hold them onto the heads to break loose, any hints? These are bolts not studs. I've only tried when the engine was cold. No way to get penetrating oil in there.

You have one of the best bolt removers at your disposal. Your mig machine. Let's say you round the head off or even break the head of the bolt off. Find a nut and weld the nut on the broken bolt(fill the center of the nut up with high heat and good feed). The heat will allow the bolt to come out. You can use penetrating oil after you weld the nut on. This may take a couple of tries but it works. Also once the nut is welded on let it cool for a little bit and rock the nut back and forth with a wrench.
T.J.

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Thanks for the replies. The bolts are probably 3 inches long & go through the exhaust manifold & then thread into the head. I don't want to break them off if I can help it. They are not seized in the exhaust manifold but in the head. Worst case I plan on cutting off the boltheads to remove the ex manifold & then maybe I can get some heat or penetrating oil on the threads. I was hoping there was a tried & true method for this application.

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ya be in bad fortune. Try tightning the bolt first. If that don't work then take the heads of the bolts off, remove the manifolds, heat the studs remaining, apply parafin or candle wax to the block around bolt stub, attach vise grips close and get it to giggle and work it out. Be patient.

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I have a set of bolt extractors, they work better in tight places. You may still need heat though. They are made by craftsman, and about $50. I would cut the heads off remove the manifold then try the extractor, for more bite.

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I'd also go with cutting the heads off to leave something to grab onto when you let the penetrating oil do its thing.

If you opt to twist them off first, you're guaranteed to part the bolts at the shank where the last thread ends (first section of minor diameter reduced from major diameter = weakest point between force applied and resistance at the threads), or worse, at the face of the head where there's next to nothing left to grip or weld to.

Heat crushes the rust by expanding the bolt inside the hole. When the bolt cools, the male thread is no longer bonded to the female head. If you heat the bolt, but don't let it cool, you risk seizing the bolt via that expansion itself. So if you get out the rosebud, get em good and hot, then let them cool.

Penetrating oil works wonders, but you need to let it soak - several hours, and sometimes days. There's a lot of pressure holding the threads together, so just getting em a little wet isn't going to allow the oil to find its way between the mating surfaces that are fused together. If you're going to heat them, do it before the oil. There's no use in burning off the oil you just applied.

And lastly, use some freaking anti-seize when you put it back together.

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We do them on occasion, my mechanic bud does them regular. Many times its easiest to cut the heads off, (grind or usually torch them) rap on the manifold and slide off over the now studs, remove them after the fact. This avoids breaking them off at the head.

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the problem is always access. if you can get at the bolts than any combination of heat, cold (like cooling the bolt with electronic contact cleaner when the threaded block is hot), and vibration (like a air hammer with a center punch like tool to put on the center of the hex and just hammer for 30 seconds or so) will do the job. in a shop setting where time is money, they would just torch the heads off and remove the manifold. then they would heat the exposed bolt stems, let them normalize, heat them again, let them normalize, then soak the base of the studs with penetrating oil while they are still hot but not so hot that the oil vaporizes right away. the penetrating oil is heat seeking like soldering flux is when sweating copper pipe. then when you break them, always use a back and forth motion trying for a little more range of motion each time.

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Apply penetrating oil, wait several hours, air hammer the head for a bit, then impact driver. If the impact driver won't spin them right out, don't break them just yet. Resort to heating the bolt to a straw yellow color and allow it to cool to a dull red before trying the impact again.

The advantage of trying to spin it off really hot is that the steel is softer and will deform as it encounters inconsistencies such as corrosion in the thread interface. The disadvantage is that since the steel is softer at this temperature, it will shear easier, most likely flush with the head. Drilling and using a screw extractor in that space is not fun at all.

80% of failures are from 20% of causesNever compromise your principles today in the name of furthering them in the future."All I ever wanted was an honest week's pay for an honest day's work." -Sgt. Bilko"We are generally better persuaded by reasons we discover ourselves than by those given to us by others." -Pascal"Since we cannot know all that there is to be known about anything, we ought to know a little about everything." -Pascal

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I second using the impact! it will shake loose a bolt that would twist off normally. I used to own a muffler shop and an automotive machine shop/garage. If you use heat then consider how shrinking works when using it.
There isn't much penetrating oil can do on a 3" bolt.
Impact and flank-drive swivel sockets working both directions with good safety gasses and holding your mouth right
You might get a friend to use the impact while you heat the head with the torch if possible also. Just don't do more damage than good.